The present disclosure relates to a fixing device which fixes a toner on a sheet and an image forming apparatus including the fixing device.
As an example of the fixing device which fixes a toner on a sheet, a sliding belt type fixing device is known. The fixing device of the type includes a pressing roller, a cylindrical heating belt, a nip plate facing the inner circumferential face of the heating belt via a lubricant and holding the heating belt with the pressing roller and a heating part which heats the heating belt. The pressing roller is pressed against the nip plate via the heating belt, and then a pressing area is formed between the pressing roller and the heating belt. When the pressing roller is driven to be rotated, the heating belt is driven by the pressure roller to be rotated. The sheet on which the toner is transferred is held and conveyed by the heating belt and the pressing roller at the pressing area. Then, the toner is pressed at the pressing area and heated by the heating part to be fixed on the sheet.
In the above fixing device, as an abrasion and a deterioration of the heating belt, the pressing roller and the nip plate proceed, a slip may occur between the heating belt and the pressing roller. If a rotation speed of the heating belt is decreased owing to the slip, the heating belt may be abnormally heated locally and then deformed. In order to prevent the abnormality, a technique is known, in which a rotation speed of the hating belt is detected by using a cap attached to the end of the heating belt and a heating value of the heating means is controlled depending on the detected rotation speed. The cap has a disk part facing the end face of the heating belt and a cylindrical part having the inner circumferential face coming into contact with the outer circumferential face of the heating belt, and is rotated together with the heating belt.
However, in a case where a large amount of lubricant is applied in order to reduce a friction resistance between the heating belt and the nip plate for a long period, the lubricant leaks from the end of the heating belt to the inner circumferential face of the cap, and a slip occurs between the heating belt and the cap. On the other hand, if an amount of the lubricant is decreased, the lubricant is exhausted at an early stage, a frictional resistance between the heating belt and the nip plate is increased, and then a slip may occur between the heating belt and the pressing roller.
Then, conventionally, a technique to inhibit the leakage of the lubricant from the heating belt is discussed. For example, an end attachment member may be provided, which has a belt end guide face to guide the inner circumferential face of the end of the heating belt. On the belt end guide face, a plurality of grooves is formed along the rotational direction of the heating belt.
However, because of a flexibility of the heating belt, a contact between the heating belt and the end attachment member is unstable, and an effect to inhibit the leakage of the lubricant is insufficient. In order to compensate the insufficiency, if the end attachment member is forcefully made to come into contact with the heating belt, the heating belt is applied with excessive stress. Then, in addition to increased risk of break of the heating belt, an abrasion of the inner circumferential face of the heating belt may occur by increase in contact pressure. Although a mechanism to detect a rotational speed of the heating belt is lubricated with a grease, because a conventional grease has a relatively high viscosity, a load is increased by viscose resistance. Additionally, because a work for applying the grease is required, there is a problem in productivity.